Semiconductor laser arrays are known as laser elements with high output. FIG. 11 is a perspective view showing an example of a semiconductor laser array. As shown in FIG. 11, in a semiconductor laser array 12, a plurality of active layers 14 are aligned in parallel.
FIG. 12A and FIG. 12B are a side view and a plan view, respectively, of laser array 12 and illustrate the spreading angles of a laser beam emitted from an active layer 14. In these figures, the x-axis, y-axis, and z-axis indicate the longitudinal direction, horizontal direction, and vertical direction, respectively, of laser array 12. Also in these figures, the number 15 indicates the central axis of a beam. For each beam emitted from an active layer 14, the spreading angle in the vertical direction is 30° to 40° (see FIG. 12A) and the spreading angle in the horizontal direction is 8° to 10° (see FIG. 12B).
In consideration of an application wherein lenses, etc., are used to condense beams from a semiconductor laser array onto an optical fiber, etc., it is preferable to restrain the spread of the respective components of the vertical direction and the horizontal direction of each beam. The vertical direction components of the beams can be collimated readily using a collimator lens. On the other hand, it is not easy to restrain the spread of the beams in the horizontal direction. This is because when a plurality of active layers 14 are positioned close to each other, the beams emitted by these active layers 14 cross each other immediately. A method of increasing the interval between the active layers may be considered for preventing the crossing of the beams. However, a high beam density cannot be anticipated in this case.